1. Field of the Invention
The invention relates to a laminated glass.
2. Description of the Background
In recent years, infrared shielding glass windowpanes have been used as automobile windowpanes increasingly to decrease the temperature rise in the compartment and the load on the air conditioner. As infrared shielding windowpanes, thin film-deposited glass sheets having thin films of various metals and metal oxides layered on the glass surfaces have been used conventionally, and these films can considerably block the entry of solar energy into the car compartment.
However, these electroconductive films can impair the function of the windowpane as a radio, TV or GPC (Global Positioning System) antenna by lowering the radio wave transmittance of the windowpane. An antenna of this kind is made of a wiring pattern (of a sintered electroconductive ceramic paste or the like) printed on the interior side of the rear windowpane. Therefore, windowpanes have to have high radio wave transmittance in order to function as an antenna.
[Prior Art 1]
As a solution to this problem, a laminated glass that transmits radio waves as well as intercepts infrared rays is proposed in JP-A-8-259279 (hereinafter referred to as ""279 publication). The laminated glass has an interlayer in which functional fine particles with particle diameters of at most 0.2 xcexcm are dispersed, and is supposed to not only intercept infrared rays but also suppress radio interference.
As one embodiment, the ""279 publication discloses a laminated glass comprising a 2 mm-thick clear glass sheet, and a 2 mm-thick green glass sheet bonded via an interlayer having ITO fine particles dispersed therein (in an amount of about 0.3 part by mass (≈0.2xc3x977÷(7+95÷323)xc3x97100) in relation to 100 parts by total mass of the interlayer) in Example 6. The laminated glass realizes a satisfactory solar transmittance Ts, 42.0%, and a haze H as low as 0.2%.
However, the content of ITO fine particles in Example 6 is too low to satisfactorily suppress near infrared transmittance and allows the surface temperatures of the car seats and the steering wheel and the temperature of the car compartment to rise.
[Prior Art 2]
On the other hand, the relation between IR cutoff properties and the amount of fine particles is described in the publication of Japanese Patent No. 2715859 (hereinafter referred to as ""859 publication). The publication mentions an infrared cutoff material comprising an organic resin and ITO powder dispersed therein and shows the relation between IR cutoff properties and the amount of ITO powder added in FIG. 1.
When the plots for Example 3 in which 8 g of ITO powder was dispersed in a solvent containing 10 g of an acrylic resin solution, and Example 4, in which 8 g of ITO powder was dispersed in a solvent containing 4 g of an acrylic resin solution, shown in the figure are compared, it is apparent that the large discrepancy between the plots for Examples 3 and 4 is attributable to the fact that the proportion of ITO powder to the resin was larger in Example 4 than in Example 3.
It is also apparent from the graph shown in FIG. 1 of the ""859 publication that the proportion of ITO powder has little influence on the light shielding properties at mid infrared wavelengths around 1500 nm (transmittance: about 5% in Example 3 and about 1% in Example 4) but does have influence at near infrared wavelengths around 1000 nm (transmittance: about 22% in Example 3 and 3% in Example 4). Therefore, the light shielding properties at near infrared wavelengths around 1000 nm improves as the proportion of ITO powder increases.
However, improvement of the light shielding properties by increase of the proportion of ITO powder can cause trouble with various communications systems using infrared rays.
For example, the VICS (Vehicle Information and Communication System) using light beacons is becoming popular in recent years in Japan. This system sends traffic information collected by an information center to automobiles and, in turn, sends information from the automobiles to the information center to prevent traffic jams. Specifically speaking, it allows interactive communications by infrared rays between devices installed on the roadside (hereinafter referred to as roadside antenna) and devices mounted on vehicles (hereinafter referred to as in-vehicle devices).
The keyless entry system allows car owners to open or close the car doors by sending infrared signals to the optical receiver installed in the car. Therefore, for proper operation of these systems, windowpanes have to transmit infrared rays, especially infrared rays at wavelengths around 850 nm which are used in these systems.
For this reason, automobile windowpanes have to satisfactorily transmit infrared rays at wavelengths around 850 nm. However, heat shielding by addition of ITO powder is problematic because the ITO powder added cuts off infrared rays at wavelengths around 850 nm as well as around 1000 nm. An interlayer having plenty of fine particles such as ITO powder particles dispersed therein has a problem of low transparency and leads to increase in the haze of the resulting laminated glass. Increase in haze worsens makes a driver""s vision worse.
As is evident from the above discussion, windowpanes that not only block infrared rays at wavelengths of from 1000 to 1100 nm contributory to temperature rise in the car compartment but also transmit infrared rays at wavelengths around 850 nm used for infrared communications are demanded as automobile windowpanes. However, sufficient interception of infrared rays within the wavelength range from 1000 to 1100 nm requires addition of a large proportion of ITO fine particles, which interferes with infrared communications systems by intercepting infrared rays at wavelengths about 850 nm as well and can cause another problem of increase in haze.
The present invention solves these problems with the prior art and primarily aims at providing a laminate glass which not only cuts off infrared rays at wavelengths of from 1000 to 1100 nm contributory to rise in indoor temperature but also transmits infrared rays at wavelengths about 850 nm used for infrared communications.
The present invention secondarily aims at providing a laminated glass with an improved appearance by suppressing increase in haze due to addition of ITO powder.
To attain these objects, the present invention provides a laminated glass comprising plural glass sheets and an interlayer interposed between the plural glass sheets, wherein the interlayer is an organic resin film having IR cutoff fine particles with diameters of at most 0.2 xcexcm dispersed therein, the product of the solar transmittances of the respective glass sheets is from 0.3 to 0.6, and the content of the IR cutoff fine particles dispersed in the interlayer is from 0.1 to 0.5 parts by mass in relation to 100 parts by total mass of the interlayer.
According to one embodiment of the present invention, the present invention provides a laminated glass according to Claim 1, wherein the solar transmittances are determined in accordance with the Japanese Industrial Standards (JIS) R3106-1998.